// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/base/division-by-constant.h"

#include <stdint.h>

#include "src/base/logging.h"
#include "src/base/macros.h"

namespace v8 {
namespace base {

    template <class T>
    MagicNumbersForDivision<T> SignedDivisionByConstant(T d)
    {
        STATIC_ASSERT(static_cast<T>(0) < static_cast<T>(-1));
        DCHECK(d != static_cast<T>(-1) && d != 0 && d != 1);
        const unsigned bits = static_cast<unsigned>(sizeof(T)) * 8;
        const T min = (static_cast<T>(1) << (bits - 1));
        const bool neg = (min & d) != 0;
        const T ad = neg ? (0 - d) : d;
        const T t = min + (d >> (bits - 1));
        const T anc = t - 1 - t % ad; // Absolute value of nc
        unsigned p = bits - 1; // Init. p.
        T q1 = min / anc; // Init. q1 = 2**p/|nc|.
        T r1 = min - q1 * anc; // Init. r1 = rem(2**p, |nc|).
        T q2 = min / ad; // Init. q2 = 2**p/|d|.
        T r2 = min - q2 * ad; // Init. r2 = rem(2**p, |d|).
        T delta;
        do {
            p = p + 1;
            q1 = 2 * q1; // Update q1 = 2**p/|nc|.
            r1 = 2 * r1; // Update r1 = rem(2**p, |nc|).
            if (r1 >= anc) { // Must be an unsigned comparison here.
                q1 = q1 + 1;
                r1 = r1 - anc;
            }
            q2 = 2 * q2; // Update q2 = 2**p/|d|.
            r2 = 2 * r2; // Update r2 = rem(2**p, |d|).
            if (r2 >= ad) { // Must be an unsigned comparison here.
                q2 = q2 + 1;
                r2 = r2 - ad;
            }
            delta = ad - r2;
        } while (q1 < delta || (q1 == delta && r1 == 0));
        T mul = q2 + 1;
        return MagicNumbersForDivision<T>(neg ? (0 - mul) : mul, p - bits, false);
    }

    template <class T>
    MagicNumbersForDivision<T> UnsignedDivisionByConstant(T d,
        unsigned leading_zeros)
    {
        STATIC_ASSERT(static_cast<T>(0) < static_cast<T>(-1));
        DCHECK_NE(d, 0);
        const unsigned bits = static_cast<unsigned>(sizeof(T)) * 8;
        const T ones = ~static_cast<T>(0) >> leading_zeros;
        const T min = static_cast<T>(1) << (bits - 1);
        const T max = ~static_cast<T>(0) >> 1;
        const T nc = ones - (ones - d) % d;
        bool a = false; // Init. "add" indicator.
        unsigned p = bits - 1; // Init. p.
        T q1 = min / nc; // Init. q1 = 2**p/nc
        T r1 = min - q1 * nc; // Init. r1 = rem(2**p,nc)
        T q2 = max / d; // Init. q2 = (2**p - 1)/d.
        T r2 = max - q2 * d; // Init. r2 = rem(2**p - 1, d).
        T delta;
        do {
            p = p + 1;
            if (r1 >= nc - r1) {
                q1 = 2 * q1 + 1;
                r1 = 2 * r1 - nc;
            } else {
                q1 = 2 * q1;
                r1 = 2 * r1;
            }
            if (r2 + 1 >= d - r2) {
                if (q2 >= max)
                    a = true;
                q2 = 2 * q2 + 1;
                r2 = 2 * r2 + 1 - d;
            } else {
                if (q2 >= min)
                    a = true;
                q2 = 2 * q2;
                r2 = 2 * r2 + 1;
            }
            delta = d - 1 - r2;
        } while (p < bits * 2 && (q1 < delta || (q1 == delta && r1 == 0)));
        return MagicNumbersForDivision<T>(q2 + 1, p - bits, a);
    }

    // -----------------------------------------------------------------------------
    // Instantiations.

    template struct EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
        MagicNumbersForDivision<uint32_t>;
    template struct EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
        MagicNumbersForDivision<uint64_t>;

    template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
        MagicNumbersForDivision<uint32_t> SignedDivisionByConstant(uint32_t d);
    template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
        MagicNumbersForDivision<uint64_t> SignedDivisionByConstant(uint64_t d);

    template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
        MagicNumbersForDivision<uint32_t> UnsignedDivisionByConstant(
            uint32_t d, unsigned leading_zeros);
    template EXPORT_TEMPLATE_DEFINE(V8_BASE_EXPORT)
        MagicNumbersForDivision<uint64_t> UnsignedDivisionByConstant(
            uint64_t d, unsigned leading_zeros);

} // namespace base
} // namespace v8
